A paper published in the British Medical Journal (BMJ) on 12 April 2016 reporting a re-analysis of the Minnesota Coronary Experiment, reportedly says that consuming unsaturated fats, such as vegetable oils, does not help to reduce the risk of cardiovascular disease. This goes against five decades of public health recommendations. Indeed, we were told that reducing intake of animal fats such as from bacon and butter, and replacing them with vegetable oils and fats, like those found in margarine and spreads, contributes significantly to heart health…
Who to believe? Does this study actually change the status of scientific evidence?
From this randomized trial, which lasted on average about 1 year, researchers found that a diet enriched in a certain type of unsaturated fat (namely ‘linoleic acid’) did not result in a reduction in mortality, even though cholesterol levels fell significantly.
There is actually nothing new to these findings. This paper is a combination of a re-analysis of the Minnesota Coronary Experiment and a meta-analysis of 5 Randomized Control Trials. The results were already reported by the original investigators in 1989 (Frantz, 1989). They are “irrelevant to current dietary recommendations that emphasize replacing saturated fat with polyunsaturated fat, including sources of both n-3 and n-6 fatty acids”, as stated by Dr. Walter Willett, Harvard Nutrition Department Chair.
There are several major limitations which could explain the association between strong drops in cholesterol and increased mortality in both diet groups. The short duration of the intervention makes it impossible to expect any cardiovascular benefit from treatment. There was also a high drop-out (only 25% of the participants received study diets for more than 1 year).
The observed strong relationship between the fall in cholesterol and increased death risk is irrespective of the treatment and most prominent in people aged 65 or above. It suggests that people who died had an illness that caused their cholesterol to fall dramatically prior to death. Weight loss or other factors such as alcoholism, smoking, drug abuse, depression or cancer might be the underlying causal factor, but they were not assessed in the study.
These findings have also been criticized by influential bodies. The British Heart Foundation stated: “We know that having too much cholesterol in your blood can increase your risk of cardiovascular disease, which is why managing our cholesterol level is crucial”. Public Health England and Heart UK also rejected the findings.
National dietary recommendations from countries such as the UK, Germany, the Netherlands and the USA are on the same line: a healthy diet should include foods high in unsaturated fats, such as vegetable oils, margarines and spreads. These recommendations are supported by a wealth of scientific research, which show that replacing saturated fat with unsaturated fat, especially polyunsaturated fat, can reduce heart disease risk.